JPH09100257A - Method of refining diaryl carbonate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a diaryl carbonate such as diphenyl carbonate in high yield and purity.

SOLUTION: A diaryl carbonate is purified by crystallizing out from a crude diaryl carbonate solution. A crude solution is cooled down to a temperature lower than the nucleation temperature of the diaryl carbonate by about 1-2°C to cause nucleation. Subsequently, the mixture of cooled at a controlled speed of about 0.01-1.0°C per minute to produce a diaryl carbonate crystal, and the remained liquid is separated. The isolated crystal is incrementally heated up to the fusing temperature at a controlled speed, and the liquid drops exuded from the heated crystal are isolated in every increment, and the molten crystal is recovered to obtain a highly purified diaryl carbonate. By repeating the process as a multistage process, the yield and purity are improved.

COPYRIGHT: (C)1997,JPO

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a method for purifying a diaryl carbonate such as diphenyl carbonate.

[0002]

Description of the Prior Art Diaryl carbonates such as diphenyl carbonate can be prepared in a number of ways. For example, one method is the phosgenation of aromatic hydroxy compounds in the presence of quaternary ammonium salt catalysts.
nation). One variation involves phosgenation at elevated temperature in alkaline solution. In the process of commercial production of diphenyl carbonate, a pH of 10
Phosgenation of phenol at temperatures of 55-60 ° C. in the presence of ca. 11 caustic.

In the commercial production of diaryl carbonates,
Regardless of the method used, various contaminant compounds are always included in varying amounts. Specific examples of contaminants that have been identified include inorganic chlorides, organic chlorides, metal ions, iron compounds, acidic compounds such as aryl chloroformates, as well as a group of compounds identified solely as "colorants". It is a compound. These contaminants often affect the use of diaryl carbonate for specific applications. For example, when it is desired to use it as a monomer reactant in the production of aromatic polycarbonate resins by transesterification (using bisphenol-A and diphenyl carbonate), the presence of contaminants can affect the rate of polymerization and the color of the resin. May have an impact. Such polymer products have a low intrinsic viscosity (VI),
May be colored in a variety of colors from pink (contaminated with iron) to brown (contaminated with phenyl chloroformate).

Distillation of diaryl carbonate is effective for removing colored substances, and although the problem of coloring in carbonate and resin made from it is solved, this method causes inhibition of polymerization rate. It is not useful for removing other contaminants. In fact, the main drawback of diphenyl carbonate by the distillation method is the loss of reactivity as observed in transesterification studies. The reason is still unclear. Also, simply distilling a diaryl carbonate such as diphenyl carbonate as a means of purification leads to a loss of a certain proportion of the product, which is an economic loss anyway.

The relatively crude diaryl carbonate containing contaminants associated with the manufacturing process can be conveniently purified in a two-step process to optimize the overall yield of desired product and contaminant removal. The first step is to wash the melt of the diaryl carbonate with water, followed by the second step of distillation. The intermediate cut taken between the first cut and the final cut (product) during distillation serves to isolate colorants and contaminants that result in low intrinsic viscosity and / or colored polymeric resin. When hot water washing is performed just prior to the distillation operation, the distilled product has improved reactivity and high purity. Washing the crude diaryl carbonate helps reduce the content of impurities, including iron, and improves the final color of polymers made from purified diaryl carbonate.

The present inventor has now discovered that the diaryl carbonate can be easily separated and purified by crystallization from a crude feed material in a molten state. Crystallization can be carried out by either a falling film crystallization method or a static melt liquid crystal crystallization method.
Generally, these two methods are fundamentally “identical” in that the melt temperature is carefully and slowly lowered to separate the crystals rich in the desired product from the impure melt. Careful reduction of the temperature from the point where nucleation occurs to a desired temperature causes the liquid to become constantly saturated with the main component, resulting in the formation of the desired diaryl carbonate-rich solid phase (crystal).

The process according to the invention for obtaining pure diaryl carbonates can be carried out continuously or batchwise, with the advantage that the product is obtained in high purity throughout.

[0008]

SUMMARY OF THE INVENTION The present invention is a method for purifying a diaryl carbonate, which comprises preparing a crude solution of a diaryl carbonate mixed with a contaminating by-product during the preparation of the diaryl carbonate, the solution being kept at a temperature higher than the nucleation temperature of the diaryl carbonate. The solution containing the nucleated diaryl carbonate is cooled by cooling to a temperature about 1-2 ° C. lower to cause nucleation.
Cooling at a controlled rate of about 0.01-1.0 ° C. per minute causes crystals of the diaryl carbonate to form in the residue of the cooling solution and separates the residue of the cooling solution from the diaryl carbonate crystals formed. The separated crystals are heated incrementally to their melting temperature at a controlled rate, separating the sweat that has exuded from the heated crystals at each increment and melting the melted crystals. Is recovered to obtain a high-purity diaryl carbonate.

In the semi-continuous process, which is one of the embodiments of the present invention, it is possible to recover a diaryl carbonate close to the theoretical yield, in which the separated droplets and the solution residue are repeatedly subjected to fractionated melt liquid crystal emission. To be recycled.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION The following description relates to preferred embodiments of the invention for the purification of diphenyl carbonate (DPC). It will be apparent to those skilled in the art that the method of the present invention can be applied to the purification of other diaryl carbonates such as di-o-cresyl carbonate and di-o-chlorophenyl carbonate.

Referring to the accompanying drawings, FIG. 1 illustrates a static crystallizer assembly 10 for carrying out the purification of diaryl carbonate contained in a crude product obtained, for example, by phosgenation of a phenolic compound reactant. A schematic diagram of is described. A portion of the melted crude diphenyl carbonate (DPC) raw material obtained as a product during production is added from the upper end 13 of the jacketed tube 12 of the crystallizer. After precooling, the temperature of the crude melt is maintained at about 1-2 ° C below the nucleation temperature of DPC in the crude mixture. Once nucleation has occurred, a heat exchange medium such as cooling water is circulated through jacketed tube 12 through inlet 14 and outlet 16 to control the rate (typically 0.01-1.0 ° C. per minute). And slowly lower the temperature. The temperature control means 18 maintains the desired temperature ramp and maintains control of the temperature within the crystallizer assembly 10, which can be verified by a thermometer 24. While the raw material liquid to be cooled continues to be saturated, crystallization proceeds to produce crystals,
The crystals adhere to the inner wall surface 22 of the crystallizer 10.

When the desired minimum temperature is reached, the bottom valve 2
0 is opened and the non-crystallizing liquid raw material residue containing concentrated impurities is discharged from the crystallizer 10. After separation of the feed residue, the temperature of crystallizer 10 is ramped up at a controlled rate to cause sweating or partial melting of the recovered crystals. Optimal swetting temperature ramps and initial crystallization temperature ramps were tested by trial and error to maximize purification efficiency in each increment or stage and maximize overall yield of the multi-stage process. To be decided. Thus, in a preferred embodiment of the present invention, the residues and droplets obtained in the high purity stage are "retrogradely added" to the feedstock in the low purity stage, such retrograde addition being a refined product. Obtained from the highest yield stage,
And until the recycle residue in the process is obtained from the lowest yield stage.

Table 1 below shows a one-stage substance distribution list of the process of the present invention by the static crystallization method. DPC content of feedstock (DPC 53.7%) and DP of melted product
Referring to the C content (DPC 96.7%), it can be seen that the desired product (DPC) is substantially purified. It is clear that a very high degree of purity can be reached if this process is carried out in several stages.

The determination of the number of stages required to reach a given purity and color and the overall yield and efficiency can be determined by trial and error.

[0015]

EXAMPLES The following examples describe techniques and processes for carrying out the present invention and show the best mode for the present inventor, but limit the scope of the present invention. It is not meant to be done. Example 334 g of crude diphenyl carbonate (DPC) raw material (DPC 53.7%) was melted and placed in the static crystallizer 10. The temperature was cooled rapidly to around 53 ° C. Nucleation is 5
It happened at 3.8 ° C. The cooling ramp was started at a rate of 0.13 ° C per minute and continued until 30 ° C was reached. At this point the bottom valve 20 was opened and the liquid residue was allowed to drain for approximately 1 hour. Thereafter, the temperature was increased by 10 ° C., at which time each level was maintained for 1 hour, during which time “sweat” was collected. Finally, after collecting the droplets at 75 ° C, the temperature was raised to 85 ° C to rapidly melt the product in one stage. High pressure liquid chromatography (HPL) of all fractions, residues and stock solutions
Each DPC content analyzed in C), in other words, recovered DP
The substance distribution of C was determined. This is shown in Table 1 below.

[0016]

[Table 1]

In a preferred embodiment of the process according to the invention, in order to recover the maximum yield of the desired DPC product, droplets 4 and 5 are added to the residue after crystallization to give a subsequent multistage treatment. It is used as a raw material solution by mixing with the raw material solution in the process or in the subsequent multi-stage treatment process.

[Brief description of the drawings]

1 shows a preferred form of device for carrying out the method of the invention.

[Explanation of symbols]

 10 static crystallizer assembly 12 jacketed tube 18 temperature control means 20 valve 24 thermometer

Claims (4)

[Claims] 1. A method for purifying a diaryl carbonate, which comprises preparing a crude solution of a diaryl carbonate mixed with a contaminating by-product during the preparation of the diaryl carbonate, the solution being about 1 to 2 above the nucleation temperature of the diaryl carbonate. The solution containing the nucleated diaryl carbonate is cooled to a temperature lower by ℃, to cause nucleation,
Cooling at a controlled rate of about 0.01-1.0 ° C./min to form crystals of diaryl carbonate in the cooling solution residue, separating the cooling solution residue from the diaryl carbonate crystals formed, Gradually heating the melted crystal to its melting temperature at a controlled rate, separating the droplets exuding from the heated crystal at each increment and recovering the melted crystal to obtain high purity diaryl carbonate, A method comprising. 2. The method of claim 1, wherein the diaryl carbonate is diphenyl carbonate. 3. The method according to claim 1, wherein
A method, characterized in that the droplets are recycled to the residue in order to repeat the described process. 4. The method of claim 1, wherein the residue is used as a crude solution prepared in a continuous process.